首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献,搜索用时 31 毫秒
1.
This paper provides an overview of models and methods for estimation of lifetime of technical components. Although the focus in this paper is on wind turbine applications, the major content of the paper is of general nature. Thus, most of the paper content is also valid for lifetime models applied to other technical systems. The models presented and discussed in this paper are classified in different types of model classes. The main classification used in this paper divides the models in the following classes: physical models, stochastic models, data-driven models and artificial intelligence, and combined models. The paper provides an overview of different models for the different classes. Furthermore, advantages and disadvantages of the models are discussed, and the estimation of model parameters is briefly described. Finally, a number of literature examples are given in this paper, providing an overview of applications of different models on wind turbines.  相似文献   

2.
孙佳妮 《海外英语》2012,(7):147-149
Most of the studies on sight translation are related to analyzing effort models.Some scholars have established effort models for interpreting activities.However,the majority of the research published in English was conducted between English and European languages.Experiments written in English on interpreting between English and Chinese are limited.The purpose of this research is to explore the problems that occurred in students’performance of sight translation with a view to improving students’performance and the training method.The results of the experiment show that ST skills are composed of two parts:linguistic capacity and delivery skills.The problems that occurred in the case study were presented as delivery problems.However,the reason for the problems was lack of linguistic transfer capacity.This study recommends that students should be trained both on linguistic capacity and delivery skills.  相似文献   

3.
Anisotropic conductive adhesive technology for electronics packaging and interconnect application has significantly been developed during the last few years. It is time to make a summary of what has been done in this field. The present paper reviews the technology development, especially from the reliability point of view. It is pointed out that anisotropic conductive adhesives are now widely used in many applications and the reliability data and models have been developed to a large extent for anisotropic conductive adhesives in various applications.  相似文献   

4.
This paper presents a method to reconstruct symmetric geometric models from point cloud with inherent symmetric structure. Symmetry types commonly found in engineering parts, i.e., translational, reflectional and rotational symmetries are considered. The reconstruction problem is formulated as a constrained optimization, where the objective function is the sum of squared distances of points to the model, and constraints are enforced to keep geometric relationships in the model. First, the explicit representations of symmetric models are presented. Then, by using the concept ofparameterized points (where the coordinate components are represented as functions rather than constants), the distances of points to symmetric models are deduced. With these distance functions, symmetry information, for both 2D and 3D models, is uniformly represented in the process of reconstruction. The constrained optimization problem is solved by a standard nonlinear optimization method. Owing to the explicit representation of symmetry information, the computational complexity of our method is reduced greatly. Finally, examples are given to demonstrate the application of the proposed method.  相似文献   

5.
Critical review in adsorption kinetic models   总被引:6,自引:0,他引:6  
Adsorption is one of the most widely applied techniques for environmental remediation. Its kinetics are of great significance to evaluate the performance of a given adsorbent and gain insight into the underlying mechanisms. There are lots of references available concerning adsorption kinetics, and several mathematic models have been developed to describe adsorption reaction and diffusion processes. However, these models were frequently employed to fit the kinetic data in an unsuitable or improper manner. This is mainly because the boundary conditions of the associated models were, to a considerable extent, ignored for data modeling. Here we reviewed several widely-used adsorption kinetic models and paid more attention to their boundary conditions. We believe that the review is of certain significance and improvement for adsorption kinetic modeling.  相似文献   

6.
Probabilistic analysis of linear elastic cracked structures   总被引:1,自引:0,他引:1  
This paper presents a probabilistic methodology for linear fracture mechanics analysis of cracked structures. The main focus is on probabilistic aspect related to the nature of crack in material. The methodology involves finite element analysis; sta- tistical models for uncertainty in material properties, crack size, fracture toughness and loads; and standard reliability methods for evaluating probabilistic characteristics of linear elastic fracture parameter. The uncertainty in the crack size can have a significant effect on the probability of failure, particularly when the crack size has a large coefficient of variation. Numerical example is presented to show that probabilistic methodology based on Monte Carlo simulation provides accurate estimates of failure prob- ability for use in linear elastic fracture mechanics.  相似文献   

7.
Using virtual reality for interactive design gives a designer an intuitive vision of a design and allows the designer to achieve a viable, optimal solution in a timely manner. The article discusses the process of making the Virtual Reality System of the Humble Administrator's Garden. Translating building data to the Virtual Reality Modeling Language (VRML) is by far unsatisfactory. This creates a challenge for computer designers to do optimization to meet requirements. Five different approaches to optimize models have been presented in this paper. The other methods are to optimize VRML and to reduce the file size. This is done by keeping polygon counts to a minimum and by applying such techniques as object culling and level-ofdetail switching.  相似文献   

8.
The high drop-out rate in upper secondary education is a major challenge to European and US educational programmes. Upper secondary education in Norway faces a similar challenge, because in recent decades, around one-third of the students drop out of the educational programmes. The majority of the drop-outs are students in vocational programmes, and a substantial number are apprentices at the workplace. With these high drop-out rates and the ensuing personal, social and economic consequences, it is vital to address how upper secondary education systems can keep students connected throughout the programmes. By thoroughly analyzing learning environments and the experiences, interactions and processes which youth deal with during vocational education, insights into how characteristics of the learning environments relate to dropping-out and connectedness may be brought into educational discussions. The case study presented in this article explores how workplaces constitute learning environments and how apprentices participate in the learning environments of work according to their dispositions, aims and life plans. The findings show that the apprentices had different agencies and that they were involved in two distinct participation patterns at the workplace: a collaborative pattern and an executive pattern. Our findings also suggest that strong agency for the vocation may keep apprentices connected throughout the educational programme, although they are aftbrded an executive participation pattern. Based on our findings, it is appropriate to raise questions as to whether an unclear agency for the vocation, together with affordance of executive participation patterns, may suggest one possible answer for the high drop-out rate among apprentices.  相似文献   

9.
To consider the bending collapse of the pipes in the latticed frames, based on the multi-scale simulation, the collapsed parts of the pipe are meshed by the shell elements as micro-scaled models, and the other parts are meshed by beam elements macro-models. The incremental displacement constraint equations for the nodes on the section between the two models are established based on the plane section premise of classical beam theory. The method to introduce the constraint equations is derived based on the Updated Largrangian method. The location of the micro-model is predicted by the stress field of the beam element, and the length of the collapsed part is adjusted by the plastic energy in the micro model. Several examples are included to illustrate the efficiency and accuracy of this method.  相似文献   

10.
Understanding life on a molecular level is greatly enhanced when students are given the opportunity to visualize the molecules. Especially understanding DNA structure and function is essential for understanding key concepts of molecular biology such as DNA, central dogma and the manipulation of DNA. Researches have shown that undergraduate students typically lack a coherent view of concepts and their relationships when studying molecular biology within instruction-based lecture with no other pedagogical applications. In this study, we have designed an experimental to investigate the effect of a hands on paper models exercise within group work (Jigsaw Cooperative learning) on student biology teachers' academic achievement and attitudes to biotechnologies. Our goal was to develop a manipulative activity using inexpensive but graphic materials. The sample for this study consisted of 42 student teachers in the department of Biology Education during the 2005-2006 academic year. We have divided the students in two different classes. One of the classes was randomly assigned as the non-paper model (control, n=21) and the other as the paper model group (n=21). In experimental group cut and paste paper models exercise within cooperative groups, in control group traditional instructional design has been applied in teaching DNA structure, Central Dogma and Recombinant DNA. The posttests of the groups in achievement and attitudes to biotechnologies show significant differences. The results indicated that the paper model group was more successful than the non-paper group.  相似文献   

11.
A new contraction joint element model for the interface in different meshes between the arch dam sections is con- structed. The study on the elastic-plastic damage constitutive model for concrete, which is applied to multi-axial stresses, is also taken. The models of the dam-foundation-reservoir system for Xingbiling and Jinping concrete arch dams, China are calculated using the proposed contraction joint elements and the elastic-plastic damage constitutive model to verify the proposed models. Results showed that the proposed contraction joint element model has a high precision in simulating the behavior of contraction joints and the elastic-plastic damage constitutive model has a high precision in simulating the behavior of the damage to the concrete.  相似文献   

12.
On dendritic cell-based therapy for cancers   总被引:3,自引:0,他引:3  
Dendritic cells (DCs), the most prevalent antigen-presenting cell in vivo, had been widely characterized in the last three decades. DCs are present in almost all tissues of the body and play cardinal roles in recognition of microbial agents,autoantigens, allergens and alloantigen. DCs process the microbial agents or their antigens and migrate to lymphoid tissues to present the antigenic peptide to lymphocytes. This leads to activation of antigen-specific lymphocytes. Initially, it was assumed that DCs are principally involved in the induction and maintenance of adaptive immune responses, but now it is evident that DCs also have important roles in innate immunity. These features make DCs very good candidates for therapy against various pathological conditions including malignancies. Initially, DC-based therapy was used in animal models of cancers. Data from these studies inspired considerable optimism and DC-based therapies was started in human cancers 8 years ago. In general,DC-based therapy has been found to be safe in patients with cancers, although few controlled trials have been conducted in this regard. Because the fundamentals principles of human cancers and animal models of cancers are different, the therapeutic efficacy of the ongoing regime of DC-based therapy in cancer patients is not satisfactory. In this review, we covered the various aspects that should be considered for developing better regime of DC-based therapy for human cancers.  相似文献   

13.
This paper presents mean fatigue lifetime predic- tion of a wire-bond structure model in power electronic module using a failure physics approach that integrates high fidelity modelling and reduced order modelling. Loading current with variable amplitudes is applied to a finite element model of simplified wirebond structures. The resulting accumulated fatigue damage due to random loads is predicted by using reduced order modelling based on failure physics, a cycle counting algorithm, and various nonlinear fatigue damage models widely used in the literature. The reduced order mod- elling approach based on failure physics uses prediction data for the electro-thermo-mechanical behaviour of the wire-bond design of a power module obtained through non-linear transient finite element simulations, in particular for the fatigue life-time of the aluminium wire attached to the silicon chip of the wire in the module. The reduced order models that capture the black box function of the accumulated plastic strain are used in pre- dicting the mean fatigue life time of the wire bond structure under random loads. One of the widely used cycle counting algorithms, rainflow counting algorithm, is used to count cycles of the temperature profile at the specific point of the wire bond structure in a power electronic module. The cycle data from the rainflow algorithm mean life time of the wire bond structure are predicted with various cumulative fatigue models. Non-linear cumulative fatigue models such as damage curve approach (DCA), double linear damage rule (DLDR), and double dam- age curve approach (DDCA), and linear cumulative fatigue damage model such as Palmgren-Miner rule are used to predict the mean fatigue life of the wire bond structure, and the results are compared.  相似文献   

14.
The growth and evolution of the knowledge network in supply chain can be characterized by dynamic growth clustering and non-homogeneous degree distribution.The networks with the above characteristics are also known as scale-free networks.In this paper,the knowledge network model in supply chain is established,in which the preferential attachment mechanism based on the node strength is adopted to simulate the growth and evolution of the network.The nodes in the network have a certain preference in the choice of a knowledge partner.On the basis of the network model,the robustness of the three network models based on different preferential attachment strategies is investigated.The robustness is also referred to as tolerances when the nodes are subjected to random destruction and malicious damage.The simulation results of this study show that the improved network has higher connectivity and stability.  相似文献   

15.
周丽  聂勇伟 《海外英语》2015,(2):140-142
The paper tries to analyze speech perception in terms of its structure, process, levels and models. Some problems concerning speech perception have been touched upon. The paper aims at providing some reference for oral English teaching and learning in the light of speech perception. It is intended to arouse readers’ reflection upon the effect of speech perception on oral English teaching.  相似文献   

16.
We developed and tested an improved neural network to predict the average concentration of PM10 (particulate matter with diameter smaller than 10 μm) several hours in advance in summer in Beijing. A genetic algorithm optimization procedure for optimizing initial weights and thresholds of the neural network was also evaluated. This research was based upon the PM10 data from seven monitoring sites in Beijing urban region and meteorological observation data, which were recorded every 3 h during summer of 2002. Two neural network models were developed. Model I was built for predicting PM10 concentrations 3 h in advance while Model II for one day in advance. The predictions of both models were found to be consistent with observations. Percent errors in forecasting the numerical value were about 20%. This brings us to the conclusion that short-term fluctuations of PM10 concentrations in Beijing urban region in summer are to a large extent driven by meteorological conditions. Moreover, the predicted results of Model II were compared with the ones provided by the Models-3 Community Multiscale Air Quality (CMAQ) modeling system. The mean relative errors of both models were 0.21 and 0.26, respectively. The performance of the neural network model was similar to numerical models, when applied to short-time prediction of PM10 concentration.  相似文献   

17.
The specification of authorization policies in access control models proposed so far cannot satisfy the requirements in workflow management systems (WFMSs). Furthermore, existing approaches have not provided effective conflict detection and resolution methods to maintain the consistency of authorization polices in WFMSs. To address these concerns, we propose the definition of authorization policies in which context constraints are considered and the complicated requirements in WFMSs can be satisfied. Based on the definition, we put forward static and dynamic conflict detection methods for authorization policies. By defining two new concepts, the precedence establishment rule and the conflict resolution policy, we provide a flexible approach to resolving conflicts.  相似文献   

18.
The failure analysis of simply supported, isotropic, square plates is addressed. Attention focuses on minimum failure load amplitudes and failure locations, von Mises' equivalent stress along the plate thickness is also addressed. Several distributed and localized loading conditions are considered. Loads act on the top of the plate. Bi-sinusoidal and uniform loads are taken into account for distributed loadings, while stepwise constant centric and off-centric loadings are addressed in the case of localized loadings. Analysis is performed considering plates whose length-to-thickness ratio a/h can be as high as 100 (thin plates) and as low as 2 (very thick plates). Results are obtained via several 2D plate models. Classical theories (CTs) and higher order models are applied. Those theories are based on polynomial approximation of the displacement field. Among the higher order theories (HOTs) HOTsa models account for the transverse shear deformations, while HOTs models account for both transverse shear and transverse normal deformations. LHOTs represent a local application of the higher order theories. A layerwise approach is thus assumed: by means of mathematical interfaces, the plate is considered to be made of several fictitious layers. The exact 3D solution is presented in order to determine the accuracy of the results obtained via the 2D models. In this way a hierarchy among the 2D theories is established. CTs provide highly accurate results for a/h greater than 10 in the case of distributed loadings and greater than 20 for localized loadings. Results obtained via HOTs are highly accurate in the case of very thick plates for bi-sinusoidal and centric loadings. In the case of uniform and off-centric loadings a high gradient is present in the neighborhood of the plate top. In those cases, LHOTs yield results that match the exact solution.  相似文献   

19.
Retrofitting of RC Slabs Against Explosive Loads   总被引:1,自引:0,他引:1  
With the increase of terrorist bomb attacks on buildings, there is a need to develop advanced retrofitting techniques to strengthen structures against blast loads. Currently, several guidelines including an Australian version for retrofitting reinforced concrete (RC) structures are available for the design of retrofitting systems against seismic and monotonic loads using steel or fibre reinforced polymer (FRP) plates that can be either adhesively bonded to the surface or near surface mounted to the concrete cover. However, none of these guidelines provide advice suitable for retrofitting structures subjected to blast loads. In this paper, numerical models are used to simulate the performance of retrofitted RC slabs subjected to blast loads. Airblast pressure distributions on the surface of the slabs estimated in a previous study are used as input in the analysis. A material damage model developed previously for concrete and an elastoplastic model for steel bars are employed in this research for modelling reinforced concrete behaviour due to explosive loads. The material models and blast loading are coded into a finite element computer program LS-DYNA3D to do the analysis. With the numerical model, parametric studies are conducted to investigate RC slabs retrofitted by either externally bonded or near-surface mounted plates or GFRP sheets subjected to blast loads. Discussion is made on the effectiveness of the retrofitting system for RC slabs against blast loads.  相似文献   

20.
The objective of this paper is to investigate the position of the resultant force in involute spline coupling teeth due to the contact pressure distribution for both ideal and misaligned conditions. In general, spline coupling teeth are in contact all along the involute profile and the load is far from uniform along the contact line. Theoretical models available in publications consider the resultant contact force as it is applied at the pitch diameter, and this study aims to evaluate the error introduced within the confines of a common approximation environment. This analysis is carried out through using finite element method (FEM) models, considering spline couplings in both ideal and misaligned conditions. Results show that the differences between the load application diameter and pitch diameter are not very obvious in both ideal and misaligned conditions; however, this ap- proximation becomes more important for the calculation of the tooth stiffness.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号